Question

I have a set of utility classes that store static const data members. Now I need to use these data members in functional classes. I am planning to use references (dont want pointers) to the static const objects, but keep getting the error below. Can you please point out the logical/technical mistake in the code?

#include <string>

class staticData
{
  public:
   static const int cs = 1;
   static const staticData data1;

  private:
   staticData(int id_): _id(id_)   //NOTE: Private constructer, static access only!!
   { }

   int _id;
};

const staticData staticData::data1(1001);

class testReference
{
  public:
    testReference(): _member(staticData::data1)
    {}

  private:
    staticData& _member;
};

invalid initialization of reference of type âstaticData&â from expression of type âconst staticDataâ

Answer 1

You’re attempting to reference a const object through a non-const reference.

Thus, the original object can be modified through the reference, as the reference is non-const, and thus you’re breaking the contract you made when declaring the object as const.

There are 2 options:

• remove the const from static const staticData data1;
• make the reference const: const staticData& _member;

EDIT:

As per your comment, you can have:

class testReference
{
  public:
    testReference(): _member(&staticData::data1)
    {}

  private:
    staticData const * _member;
};

This way, you can change what _member points to (not possible with references), but you can’t change the object itself.